Technical Field
The invention relates to a method for determining deformations of a geometric body and a method for measuring forces or torques acting on a geometric body with the aid of force measuring sensors or deformation measuring sensors. The invention also relates to a corresponding measuring system.
Background Information
In a wide variety of technical applications, information on forces or torques, which act on a body, for example, a tool or a work piece or a tool holding device or the like, or information on deformations of the body caused by corresponding forces or torques, constitute important parameters, which are measured and/or monitored. Thus, applications are known, for example, in which corresponding force sensors or deformation sensors are used to check the correct planar contact and clamping of a tool in a spindle head of a working spindle of a processing machine. Such a method and corresponding monitoring device are described in EP 1 889 685 A1. Here the corresponding monitoring is used in order to identify potential faulty clampings of the machining tool, such as, for example, may be caused as a result of a chip that has penetrated the spindle head or the like. Such a faulty clamping, as described in the publication, results in trajectories of the machining tool that deviate from the set trajectory, and thus to a defective machining of the workpiece, ultimately to losses in quality and finally to rejection.
A further application, in which a corresponding determination of deformations of a geometric body, or the measurement of forces and torques (torsional moments) acting on these bodies plays a role, is described in EP 2 103 379 A1. Here, measured forces or torsional moments are employed for monitoring a machining operation, for example, for detecting whether a tool is being advanced on the workpiece at a desired feed force along the machining path.
One problem in connection with the methods and measuring systems disclosed in the aforementioned publications is that distorted measurement results may frequently occur due to imprecise knowledge about the orientation of the acting forces and torques, or about components thereof, or of the direction of deformation along different coordinate directions. Thus, for example, when monitoring forces or torques, as is described in EP 2 103 379 A1, it is impossible to distinguish in different situations between actual measurement values and system error-related artifacts. Nor, with regard to the measurement technique and measuring system disclosed in EP 1 889 685 A1, is it possible, because of this fact, to invariably and reliably detect all, let alone just minor, deviations and faults with respect to the clamping of the tool emphasized therein.
One option is described in DE 40 09 286 C2, with which a more precise monitoring or measurement of the torsion of a rod-shaped hollow body may be achieved with the aid of resistance strain gauges. For this purpose, variously aligned resistance strain gauge sensors are disposed on a membrane surface attached to the interior of the hollow body, and the former are interconnected with their signal outputs in a bridge circuit. Given the fact that the membrane is deformed in two directions when the pipe is torqued, an amplification of the total signal is achieved as a result of the canny interconnection of the sensors with their signal outputs in the bridge circuit, and with that, an increase in the sensitivity of the measuring unit. Even with this approach, however, the deformation or an applied torsion is monitored along only one spatial direction, in this case along a rotary coordinate direction.